Conventionally, a liquid crystal display device that carries out a full-color display achieves a full-color display by dividing each pixel of a transmissive liquid crystal display element into three picture elements, attaching red (R), green (G), and blue (B) color filters to the three picture elements, respectively, irradiating the three picture elements with white light from a backlight, and controlling, according to a signal representing a voltage applied to a liquid crystal cell of each picture element, the transmissivity of the white light passing through that picture element.
However, since each of the R, G, and B color filters transmits light of wavelengths in its corresponding wavelength range and absorbs light of wavelengths in the other wavelength ranges, such a liquid crystal display device using color filters loses approximately ⅔ of the light and therefore has a low level of efficiency in the use of light. Although there is a color-filter-free full-color display method called a field sequential color method, this method suffers from color breakup.
Meanwhile, there has been proposed a display device based on a transmissive modulation element and including a backlight device that achieves improved efficiency in the use of light in a case where LEDs (light-emitting diodes) are used as backlight light sources (see Patent Literature 1). This display device includes: an image display element (liquid crystal panel), which has openings arrayed two-dimensionally and capable of controlling the ratio of transmitted light independently for each color; a light-path-combining optical system, which has a two-dimensional array of a large number of pairs of microlenses acting as convexo-convex lenses; a lighting optical system, which emits different colors of chief rays to the light-path-combining optical system at different angles; and a plurality of light sources, which emit different colors of light.
Since the display device of Patent Literature 1 can be configured such that the action of the lighting optical system allows the colors of light from the light sources to enter the light-path-combining optical system at chief ray angles differing from one color to another and the refracting action of the light-path-combining optical system allows the colors of light to be focused onto their corresponding openings of the image display element, it is possible to divide each pixel into three picture elements and focus different colors of light onto the picture elements, respectively (color separation of each pixel according to color of light). Therefore, according to Patent Literature 1, there will be no need for a color filter, nor will there be a loss of light, provided that an ideal color separation is achieved. Note, however, that Patent Literature 1 does not exclude provision of a color filter for preventing colors from being undesirably mixed due to light leakage when the color separation is below the ideal.